I'd
put off the task of transferring my 35mm colour slide/ B&W
negative collection into digital format for far too long because
the whole process of operating my flatbed scanner ( no names no
packdrill ) was so long winded that the notion of sitting beside
my PC for a week didn't appeal one bit......... Even dedicated
35mm film scanners incur significant operational times, so it
seemed a sensible move to employ the digital camera which has
improved dramatically in recent times. Their obviously welcome
snapshot capture times plus the automatic transference of each
image file onto the SD/CF card without further ado makes for a
potentially efficient way of archiving 35mm colour slides and
negatives that is too irresistible to ignore.

The
original 35mm transparency slide copier.....the sort that
projected its imagery onto a 36mm x 24mm film plane in an SLR
works just as well with something like a Nikon D700 FX format
camera since the optical arrangement suits the full framed
digital camera as did the older film SLR. For the DX format
digital camera with a sensor about half its size the old copier
doesn't work since it projects an image which is far too large.

As I
see it there are 3 options for the DX format photographer wishing
to copy slides with their camera:-

1)
Cobble together an assemblage of extension rings, taking lens and
makeshift slide holder to perform the task.

My
first efforts started with the Sony NEX body and an M42 Pentax
35mm f3.5 film camera lens plus extension rings.

After
some experimentation with various lengths of M42 extension rings
I finally found the correct slide/lens/sensor relationship to
cover the sensor and no more. The arrangement of parts is
depicted below:-

The taking lens is
roughly in the middle and was able to reduce the 35mm film frame
onto the NEX's sensor without wasting too many pixels. The focussing
collar of the Pentax lens allows some leeway of adjustment in
this setup which is devoid of any subtlety that a bellows
extension could afford the photographer. Fortunately I managed to
achieve the scaling of image onto the sensor with just a little
room to spare. I'd luckily possessed several M42 rings from different
manufacturers, so that no 2 rings were exactly the same
length. This allowed more subtle control of the taking lens's
position which was more likely to be successfully resolved than
would have otherwise been the case had I just a single set of
rings.

The front plate that supports the
slide was fashioned from a scrap piece of brass which was epoxy
bonded to the first coupling tube. A plastic alignment piece
was cut from scrap and also epoxy bonded to this plate, and
simple microscope styled stage clamps allowed easy slide insertion but
with some adjustment slippage too. The front assembly yaws either
way by loosening one screw of the lens coupler to facilitate accurate
parallel frame edging to sensor edging, and also allows subtle
centering adjustment. The assemblage squats securely on the bench
enabling most forms of illumination to be employed in front of
the slide plate in preference to daylight if that is preferred.

2) The
More permanent Version

For very
small money an old redundant 35mm film slide copier can be
obtained. The principle task is to reduce the image scale so it
fits neatly onto the DX sensor. The distance therefore from internal
lens to sensor plane must be reduced AND the distance of the 35mm
slide holder to the lens must be increased. Since the
balanced optical see saw symmetry in the original 35mm SLR copier
is going to be upset after adaptation, the zooming mechanism the
copier might have originally sported will become defunct. However
it will by default become an accurate fine focusser of the image
onto the sensor.

The
diagram above shows a simplified ray diagram of the original
symmetrical 35mm to 35mm layout and that required for the 35mm
slide to the smaller DX sensor. Note the relative changes of the
position of the slide plane and camera DX sensor plane. The
principle is quite simple, but the gauging of the distances
requires sub-millimetre accuracy by careful measurement. Any
deviation of the image size on the camera's sensor from
inaccurate measurement cannot be corrected later by the shifting
of the internal lens.

The above
image shows a "Panagor" zoom 35mm slide copier made for
the old film SLR after modification. The original centre
piece with its internal shifting lens remains unaltered, but
the camera end ( B ) has been shortened by simply 'losing' any
part of the internal/external tubing which is of no use by means
of hacksawing and filing to finish, or by basic lathe work. All
that matters is that this shortened fixture 'B' can be still
attached to both camera and centre piece as originally made. I
employed epoxy resin to bind all the modified interlaced circular
rings firmly together.

In order
to extend the slide holder distance from the internal lens I
simply inserted a piece of alloy tubing ( A ) which I'd rebated
at both ends to suit both the centre piece and slide holder
respectively.

Determining
the lengths of 'A' and 'B'

This is of
course the critical part of the modification. Placing the
slide/lens/camera in situ, and then altering their relative
positions whilst monitoring the live view/screen on camera in
such a way that the 35mm slide's image is captured in its
entirety on the live view screen of the camera seems the easiest
route to success.

I biased the set of
the internal lens towards the camera, but not all the way, and
then PVC taped the adjusting ring to the body so that it couldn't
shift during the measuring phase. I should emphasise the simple
fact that once these measurements are determined and the
alterations carried out, the size of the image on the camera's
sensor cannot be changed by the shifting of the internal lens
afterwards: the latter will now only alter the image's focus
condition. I'd also advise anyone to refrain from 'gluing' up any
alteration until they are completely satisfied that the
combination will raise the desired image size on the sensor.
Being mindful of keeping the pieces 'square faced' whilst gauging
and measuring the important A & B distances ensures more
accurate results.

3) The contemporary
DX slide copier

I've no
knowledge or experience of this device other than that it
presumably works by insertion of a close up auxillary optic
between the slide and front element of the camera's normal zoom
lens. Its obviously a very convenient way of doing the job at a
fair price, but I wonder about the quality of the internal optic
which must by necessity be large enough to cover the relatively
wide front element of a modern 52mm filter threaded zoom lens?

In
Use/Handling

I started trials by
pointing the copiers toward the sky through a window to provide
sufficient illumination. With such a simple technique I found
myself experimenting with various illumination setups then
discovered that a sheet of white paper resting on the window
ledge beneath a bright sky was much easier to cope with over an
extensive period of time. The results were consistent with a
given white balance setting. Because of the inherent rigidity of
the assemblage there was no need for steady hands during a
longish exposure time..............though I confess that a
lifetime of camera usage had me subconsciously trying to hold the
combo motionless during the slow exposures!

Potential
Problems

Field/Film
flatness: As many readers will be aware, the flatness of
mounted colour slide film varies considerably, often tending to
dish out either side of the film plane. Since all taking lenses
have inherent curvature of field to a greater of lesser degree,
it seemed perfectly logical to mount the slide orientated to make
use of this characteristic. So regardless of the correct viewing
side I arranged each slide so the peak of its bellied film was
furthest away from the taking lens. This aids flatfield imaging,
and any reversal of the image thus incurred could easily be
corrected later in software.

Depth
of Field: I was rather surprised by the apparently larger
depth of field in this setup than I had expected. I say
apparently because the lens doesn't elicit the same crisp in and
out of focus experience of conventional photography, since both
the subject and back focus distances are similar. The effect is
to physically draw out the focussing process. Stopping down the
taking lens's aperture exacerbates this and so DOF problems
shouldn't cause any problems at all. Incidentally the aperture
value of most of the internal lenses installed in 35mm slide
copiers of the past is around f11-16 or so. This not only
increases DOF but also decreases production costs in one stroke.

The
issue concerning the taking lens quality and its effects on post
processing

In
photographic days of old the silver grain particles of B&W
film imagery formed the bedrock of an image. An enlarged print
from that era revealed the quality of imagery projected by the
camera lens as well as the quality of the imagery of the grain
structure that the enlarging lens generated in the printing
stage. Of course both were influential in controlling the
character of the final print. I mention this because there is one
dissimilarity between film and digital imagery which I believe
important enough to raise here. Silver halide grain particles and
the granular appearance of noise inherent in digitally processed
imagery are entirely separate entities, though they may look
vaguely similar. But the discreteless process of optical
enlargement cannot be imitated in digital imagery other than by
mathematical algorithms. Thus the resizing of digital imagery for
onscreen presentation incorporates both the original pixel
information intermingled with infiltrated noise. If the original
subject is a film colour slide there will be some indication of
its grain structure to be taken into account too, which
inevitably prejudices the image's quality during resizing,
assuming of course that the taking lens's quality is sufficient
to reproduce the grain structure in the first instance.

Fortunately,
the process of creating an acceptable digital image from a colour
slide or B&W negative can be successfully accomplished by
using a half decent lens, then stopping it down a fair way to
ensure the whole imperfectly flat film emulsion is captured in
even focus. After resizing, the image can be sharpened to create
a credible result with fewer artifacts than might have otherwise
been the case had the resizing algorithm dealt with totally
unnecessary detail involved in resolving the film's grain
structure and the inevitable electronically generated noise too.
The results from this simple process comfortably exceeded my
expectations from both slide copiers described above in 1) &
2). Incidentally the quality of the inbuilt taking lens of the
professional slide copiers is more than adequate, projecting even
into the corners an image which won't disappoint.

Illuminating
the slide

For most
slides that have been properly exposed a simple reflective light
source such as a sheet of white paper resting on a flat surface
next to a window is adequate with appropriate white balance
control.

Contrasty
slides can be partially tamed by a more immediate diffuse light
source, which incidentally many professional copiers employ.
There is also a very useful secondary curative property of this
diffusion screen: It helps to suppress the imagery of small dust
particles and fine scratches as well as fungal growths embedded
in the emulsion layers. It does this by drowning the high
contrast diffraction patterns that surround the minute particles
of opaque detritus by virtue of its oblique light pathways. The
main pictorial information is essentially unaffected since the
dye layers that generate the image do so by colour
differentiation and varying density only. The efficiency of the
diffusion screen in this scenario is determined by its proximity
to the colour slide. The closer it is to the rear of the slide,
the more effective it seems to be.